Licensing is quite simple once you understand the terms you and your client want. There are two types, Rights Managed and Royalty Free. If you want to make money, RM is the way to go, and if you want to sell bulk, RF is the way to go.
The number one thing is understanding how the images/video are going to be used, what media space they'll live in (print, web, tv, film etc), how long they'll be in use, and whether or not they are exclusive or non-exclusive to the client. All of these aspects are incredibly important when understanding how much you should charge.
The game has changed quite a bit in the last 10 years thanks to cheap stock sites like Adobe, Pond5, Getty, and iStock (all horrible), which makes it very difficult to charge what the image or video is likely worth. That being said, never sell yourself short on what you should be valuing your work at.